AP Chem Unit 3

Intermolecular Forces (IMF)

Forces of attraction between molecules; weaker than intramolecular bonds; determine physical properties.

London Dispersion Forces (LDF)

Temporary dipoles induced by electron fluctuations; present in all molecules; stronger in larger, more polarizable molecules.

Van der Waals Forces

General term for intermolecular forces (LDF + dipole-dipole); do not use synonymously with London dispersion forces.

Dipole-Dipole Forces

Attractions between the positive end of one polar molecule and the negative end of another; stronger than LDF in molecules of comparable size.

Ion-Dipole Forces

Attraction between an ion and a polar molecule; stronger than dipole-dipole; important in dissolving ionic solids.

Hydrogen Bonding

A strong intermolecular force between a hydrogen covalently bonded to N, O, or F and the lone pair on another N, O, or F atom in a different (or same) molecule.

Ionic Solid

A solid consisting of cations and anions held by electrostatic forces; high MP/BP, brittle, conducts electricity only when melted or dissolved.

Molecular Solid

A solid composed of discrete molecules held by IMF; low MP, does not conduct electricity.

Covalent Network Solid

A solid where all atoms are covalently bonded in a continuous 3D network (e.g., diamond, graphite, SiO₂); very high MP, rigid.

Metallic Solid

A solid consisting of metal cations in a sea of delocalized electrons; conducts electricity and heat, malleable, ductile.

Amorphous Solid

A solid without a regular, ordered particle arrangement.

Crystalline Solid

A solid with particles arranged in a regular, repeating 3D lattice.

Vapor Pressure

The pressure exerted by a substance's vapor in equilibrium with its liquid; determined by strength of IMF (stronger IMF = lower vapor pressure).

Boiling Point

The temperature at which vapor pressure equals atmospheric pressure; directly related to IMF strength.

Melting Point

The temperature at which a solid transitions to liquid; generally correlates with IMF strength.

Ideal Gas Law

PV = nRT; describes the behavior of an ideal gas where molecules have no volume and no intermolecular forces.

Partial Pressure

The pressure exerted by one gas in a mixture; proportional to its mole fraction.

Dalton's Law of Partial Pressures

P_total = P_A + P_B + P_C + …; total pressure is the sum of partial pressures.

Mole Fraction (X_A)

The ratio of moles of component A to total moles in a mixture; X_A = moles A / total moles.

Kinetic Molecular Theory (KMT)

A model explaining ideal gas behavior: gas particles are in constant random motion, have negligible volume, and elastic collisions; average KE proportional to Kelvin temperature.

Maxwell-Boltzmann Distribution

A graph showing the distribution of kinetic energies (or speeds) of gas particles at a given temperature; broadens and shifts right at higher temperatures.

Average Kinetic Energy

KE = ½mv²; proportional to absolute temperature (Kelvin); all gases at the same temperature have the same average KE.

Real Gas Deviations

Real gases deviate from ideal behavior at high pressures (particle volume matters) and low temperatures (IMF matter); both cause deviations from PV = nRT.

Molarity (M)

Concentration expressed as moles of solute per liter of solution; M = n_solute / L_solution.

Solution

A homogeneous mixture of two or more substances; macroscopic properties uniform throughout.

Solubility

The maximum amount of solute that dissolves in a given amount of solvent at a specific temperature; governed by "like dissolves like" (similar IMF).

Chromatography

A separation technique that exploits differential intermolecular interactions between mobile phase components and a stationary phase to separate mixture components; more polar components travel less far.

Electromagnetic Spectrum

The range of all electromagnetic radiation ordered by frequency/wavelength; microwave = rotational transitions, infrared = vibrational transitions, UV/visible = electronic transitions.

Planck's Equation

E = hν; relates the energy of a photon to the frequency of the electromagnetic radiation.

Speed of Light Equation

c = λν; relates the speed of light to wavelength and frequency.

Beer-Lambert Law

A = εbc; absorbance (A) equals the product of molar absorptivity (ε), path length (b), and concentration (c); absorbance is proportional to concentration at fixed path length and wavelength.

Molar Absorptivity (ε)

A constant describing how strongly a chemical species absorbs light at a specific wavelength.

Spectrophotometer

An instrument that measures the absorbance or transmittance of light through a solution; used to determine concentration via Beer-Lambert Law.